An intelligent label using sodium carboxymethyl cellulose and carrageenan for monitoring the freshness of fresh-cut papaya

A novel intelligent label (CNCB) was prepared by casting and drying a mixed solution of sodium carboxymethyl cellulose (CMC-Na) and carrageenan, to which bromothymol blue (BTB) was fixed as the pH indicator. The CNCB label can reply the freshness of fruit through color changes according to the CO2 concentration inside the package. Variations in the three label components were investigated using Fourier transform infrared spectroscopy. Furthermore, the label morphology and structure were evaluated using scanning electron microscopy and X-ray diffractometry. Lastly, the thermal stability of the labels was analyzed using a synchronous thermal analyzer. Carrageenan enhanced the water resistance of the CMC-Na label and improved the mechanical properties. Moreover, while the BTB dye was added to visually indicate color change, its addition improved not only the physical properties but also the thermal stability of the label. The CNCB label showed different color changes in response to different CO2 concentrations. When the CNCB label was stored with fresh-cut papaya, its color changed from blue to green, yellow-green, and eventually yellow-brown as the fruit lost its freshness, displaying a strong correlation with the CO2 concentration in the package. This label prepared from CMC-Na, carrageenan, and BTB, can be used as intelligent label in monitoring the freshness of fresh-cut papaya for the excellent pH sensitivity.